Geographic Information Systems
The GIS software industry is rapidly growing. Although the components of GIS software are simple to purchase, the expertise to properly allow these systems to function is often underestimated, and the proper data compilation is expensive and time-consuming. Simply put, a GIS is any information management system that can:
- Collect, store and retrieve information based on its spatial location
- Identify locations within a targeted environment, which meets specific criteria
- Explore relationships among datasets
- Spatially analyze the data within each environment
- Display the selected environment numerically and graphically before and after analysis.
All of this data is georeferenced, that is, linked to a specific location on the surface of the Earth through a system of coordinates. To many, one of the easiest coordinate systems to work with in terms of projection is latitude and longitude. A GIS is not isolated to objects and their positions; it can also incorporate properties of these objects as additional data within the system.
The key to a successful GIS is the foundation on which it is built. Proper planning in the early stages of GIS creation cannot be overlooked or underestimated. Money saved in the early stages of producing a GIS is usually spent fixing something else down the road. Money does indeed need to be spent—but spent wisely.
Coordinate Systems for GISWhen a GIS is created, some foresight is required as to the desired coverage of the maximum area. If this can be established, the surveyor can predict the middle of the GIS and scale the coordinate values from that point outward to fit the ground. This beginning step is very critical and sometimes not fully understood. Every project I have worked on except one has requested State Plane Coordinates, however the GIS operators and managers do not understand the difference between grid and ground values. Following the Arizona Revised Statute, state plane values are at the grid not on the ground, therefore distances measured between these points are generally short by a factor of 0.9997 international feet. When a State Plane Coordinate is fit to the ground it is no longer considered a State Plane Value, therefore that value must be modified or truncated so it won’t confuse the user.
Local coordinate systems are most often the best systems to use for reproducible maps. Creating a system with compound scale factors or negative coordinate values becomes cumbersome to end users. Using local coordinate systems from the beginning eliminates the confusion between grid and ground, and provides easier and smaller coordinate values in which to work. If the desire to establish a real world Earth-centered, Earth-fixed position exists, a GIS can simply output WGS 84 latitudes and longitudes with local heights. These values can be converted to State Plane Values or local coordinates very easily with today’s software.
The Question of AccuracyThe question of accuracy of GIS has been the most storied between the surveyor and the GIS specialist. While surveyors are expert measurers and reporters of rights upon the ground, GIS practitioners have introduced the terms “mapping grade” and “sub-meter.” It has been my experience that the only cost difference between these two categories is the equipment used in the data acquisition process to establish a “survey-grade” network versus a “mapping-grade” network.
There are many variations of this theme. A network can be established for the entire boundaries of the GIS using survey-grade technology. At this point mapping-grade data can be gathered within this network with higher rate repeatability than that of a strictly mapping network. However, any mapping-grade data may be sub-meter within itself, but these results cannot be repeated at future visits. This means that if on Tuesday a user gathers a manhole at mapping grade at point “A,” and returns on Wednesday, Point “A” will be in a different spot and a different one on Thursday, and so on. It is the choice of the user whether to accept these results. Equipment dealers and sales people often neglect to inform the user of this slight discrepancy. Using survey-grade equipment to gather the value, the confidence level of the repeatability of that position goes up exponentially.
For most attributes, the high level of accuracy may not be desired or required. It would be a very good decision to place the higher level of accuracy on the land base or the coordinate geometry of the property lines. With the increased use of private individuals using the GIS for property map reference, increased awareness to improving the accuracy of the land base is desirable.
Data ManagementIn my view, one of the most overlooked variables in the data acquisition and data management areas of GIS has been the operator’s experience level. With GIS technology rapidly changing, a student of the curriculum will arrive at work ready to operate the software. The same is said about today’s young surveyor. “COGO in a yellow box” is what I call it. With the data collectors and computers of today, our technicians are gaining the ability to push buttons, but does anyone explain to them what these buttons mean?
The surveyor, a.k.a. expert measurer, gathers spatial data from such objects as manholes, valves, culverts and signs. While acquiring this data, additional information can be input through a data dictionary. The inexperienced surveyor will input what the data dictionary asks him to input—no more, no less. This data is then downloaded, processed and delivered to the GIS technician for input. From this point, the GIS technician observes two water valves on a curved street on the screen and then draws a straight line between them running through the mayor’s front yard. At the council meeting presentation, the technician’s boss will need to explain why this occurred or he won’t be a boss much longer.
I try to emphasize that the people we place in charge of gathering and implementing data depend on us to provide them with the explanation of what it is. If we do not have the experience, it is up to us to get it for them. Let them observe a survey or construction project. They need to see water lines and sewer lines installed in the ground around a curve to understand that it is possible to deflect pipe in that manner. In my view, several GIS technicians are not experienced enough to manage data. They may have the ability to manipulate the software, but do not comprehend that knowledge beyond their computer screen may be required at times. Accordingly, the surveyor must provide as much detail as he can regardless if it has been requested. This will at the very least cause the GIS technician to ask questions.
Where Does Surveying Fit in the GIS World?At a chapter meeting of the APLS last year, attendees discussed GIS. A veteran of the area made this statement: “Unfortunately, I feel that GIS is something that has passed us (surveyors) by.” This is not the major consensus in the surveying community. I have discovered that many think the time is now for members of these two professions—surveying and GIS—to integrate. Surveyors need to utilize GIS for its real potential and GIS specialists need to utilize surveyors for their potential.
Communities and utility companies of varying size have become part of the GIS explosion in Arizona. Cities like Tempe and Tucson have developed some of the more complete GIS databases. Other communities are following their examples. One hurdle is that Tempe and Tucson established their parcel bases to a survey level, which was an expensive undertaking but has paid dividends for the end user, the public. Other communities depend on outside agencies for the development of the parcel base. This is considerably less expensive, but provides for numerous questions as to the accuracy of the GIS. Some GIS technicians feel that if they did not input the data but are simply manipulating it, they cannot be held accountable for its quality, an attitude that is decreasing but still present.
The inevitable requirement of state registration for GIS is on the horizon. What form it will take is yet unclear. With this in mind, the two professional communities must join forces. We need to share our wealth of knowledge and understanding with each other in order to ensure that proper registration guidelines are in place when the time comes. Many GIS professionals look at registration requirements as regulation. I see it as a way to protect the public, which is the ultimate goal of any registration body.